The significance of diffusion coefficients

In the development of estimation methods for D values, two independent contributions must be taken into consideration on one side, the size and shape of the per- 

When one plots the D values of various different compounds versus their relative molecular mass, M, for a given polymer, then the values for the n-alkanes lie on the upper limit of diffusion (Fig. 9-8). This result means in practice that one has a maximum value for a variety of compounds with similar molecular weights when the n-alkane diffusion coefficients are known. In a first approximation one can assume the ratio of the D values between a gas, for example carbon dioxide, and a n-alkane with the molecular weight Mr to be constant and independent of the polymer. Given the existence of values for simple gases in a large number of polymers (Table 9-2) the 

Equation (9-16) is valid for permeation through laminate structures. 

The above example underscores once more the importance of distribution processes between the packaging and products which does not occur in the case of simple gases with very low solubility. 

Tabic 9-17 Partition coefficients K 102 of 7 aroma compounds with different polarities between a laminate PE/Ad/OPP with 62 pm thickness (40/2/20) and methanol at 23 °C. 

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